Molecular signatures of microbial metabolism in the marine water column

My research focuses on the use of molecular signatures to investigate microbial metabolic diversity and function in the deep ocean and how this impacts carbon and nutrient cycling. Marine microbes are important in many processes of biogeochemical cycling in the ocean, both within distinct ecosystems and on a global scale. In particular, the roles marine microbes play in the chemistry and cycling of marine dissolved and particulate organic matter (DOM and POM, respectively) have important implications for the sequestration of CO2 in the deep ocean. However, many unanswered questions remain about the metabolic mechanisms employed by marine microbes, especially below the euphotic zone and within the bathypelagic region from 1000 to 5000m depth. In order to fully understand biogeochemical cycles in the ocean, it is necessary to understand the various ways that microorganisms can interact with and transform POM and DOM in this region of the water column.
Because more than 90% of marine microbes remain uncultured, culture-independent techniques are essential to study these organisms in the context of their environments. A growing number of studies are combining phylogenetic and lipid biomarker analyses to improve both coverage and resolution of microbial metabolic diversity, and aid in the identification of biogeochemical niches occupied by these diverse groups. Lipid biomarkers are particularly useful because not only are they often specific to certain microbial groups or metabolisms, they tend to persist in the environment longer than other biomolecules- even up to millions of years in the fossil record! They also retain their isotopic compositions over long timescales, which can be used as tracers of metabolic processes and energy transfer.

My current projects in this area include:

    1. Investigating the diversity of bacterial lipids called hopanoids and their microbial producers in marine POM across oxygen gradients in the California Current region.
    2. Investigating the genetic diversity of other genes involved in the hopanoid biosynthetic pathway, such as the recently identified HpnP methylase (Welander, Coleman, Sessions, Summons, & Newman, 2010), in low oxygen environments
    3. Exploring the variability in the D/H ratio of lipids in marine POM from a range of different environments and biogeochemical regimes, and to evaluate the usefulness of D/H ratios in fatty acids as a means of examining the biogeochemical processes contributing to and transforming POM.